* you pruned it at the wrong time of the year (it produces flower buds for Spring in July-ish so -for example- pruning in or after July 2012 cuts the blooms that will open in Spring 2013),

* if you feed it too much fertilizer (1/2 cup to 1 cup of compost, composted manure or cottonseed meal in May and July in the south is enough; once in June in the norther half of the country is also enough for the whole year; can also use a general-purpose slow-release chemical fertilizer like Osmocote on those same dates),

* if you plant it where it is too cold (Zone 5 winters or colder may start killing flower buds so winter protection may be necessary; make sure it has 3-4" of mulch year around up to the drip line) or

* if you hard prune it drastically (it may either not bloom or may bloom just a fraction of normal on the next year; it will revert back to normal blooming after taking that one year break).

* you pruned it at the wrong time of the year (it produces flower buds for Spring in July-ish so -for example- pruning in or after July 2012 cuts the blooms that will open in Spring 2013),

* if you feed it too much fertilizer (1/2 cup to 1 cup of compost, composted manure or cottonseed meal in May and July in the south is enough; once in June in the norther half of the country is also enough for the whole year; can also use a general-purpose slow-release chemical fertilizer like Osmocote on those same dates),

* if you plant it where it is too cold (Zone 5 winters or colder may start killing flower buds so winter protection may be necessary; make sure it has 3-4" of mulch year around up to the drip line) or

* if you hard prune it drastically (it may either not bloom or may bloom just a fraction of normal on the next year; it will revert back to normal blooming after taking that one year break).

No, that will not help. If you live in Z5, the shrub is planted out of zone. You need to either grow it in a pot that stays indoors during winter or you need to winter protect the plant.

This hydrangea creates flower buds during the July-August time frame. These flower buds are invisible and will open in Spring 2013 but here is the problem... the stems die out during winter because it gets too cold for them. When the stems die, so do the flower buds in them. The roots, however, survive as they are protected underground so the plant grows new stems in Spring. And the cycle repeats.

As soon as the plant begins to go dormant, use chicken wire to cage it. The chicken wire can then be filled with straw or dried out leaves. Make sure that the ends of the stems have at least 6" between them and the chicken wire (sideways and at the top). To make sure the leaves do not fly off, put a cardboard on top, with a few bricks or rocks to hold it in place. The top of the plant should be about 6" or more underneath the cardboard in order to protect stems that are growing upwards. Pack as much straw or as many leaves as you can. The more you have, the better insulated the plant is. Most of the flower buds are at the end of the stems so this is the area to protect. In the middle of winter, add more leaves or straw as settling usually occurs by mid winter; check the sides and the top to maintain the 6" of separation (or more).

You are close to that point in time when you need to protect so feel free to buy the ingredients now (the chicken wire, straw, etc). You can most dried out leaves that you can find too. Some people place the chicken wire around the shrub as soon as Fall starts and then wait for the plant to begin showing signs of dormancy before adding the leaves or straw.

Winter protection can be removed in the Spring, about two weeks after your average date of last freeze. The straw can then be used as mulch or dumped in the compost pile. The leaves can go in the compost pile. Sometimes the stems will look white-ish when you remove the winter protection but that is ok. It occurs when the weather is warm and the plant awakes and puts on growth while still winter protected.

The variegated forms - 'Mariesii Variegata' in particular - are not known for producing abundant flowers. Even in my mild zone 8 climate where winter protection is unnecessary they bloom very sparsely. IMO, these are valued much more for their gorgeous foliage effect than they are for their flowers.